Extraction of Sodium and Potassium Perchlorates with Dibenzo-18-crown-6 into Various Organic Solvents. Quantitative Elucidation of Anion Effects on the Extraction-Ability and -Selectivity

Abstract

The constants for overall extraction into various diluents of low dielectric constants (K ex ) and aqueous ion-pair formation (K MLA ) of dibenzo-18-crown-6 (DB18C6)–sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25°C. The K ex value was analyzed by the four underlying equilibrium constants. The K MLA values were determined by applying our established method to this DB18C6/alkali metal perchlorate extraction system. The KM(DB18C6)A value of the perchlorate is much greater for K+ than for Na+, and is much smaller than that of the picrate. The K MLA value makes a negative contribution to the extractability of DB18C6 for MClO4, whereas the value of the MLA distribution-constant does a major one. The partition behavior of M(DB18C6)ClO4 obeys the regular solution theory. However, the M(DB18C6)ClO4 complexes in the diluent of high dipole moment somewhat undergo the dipole–dipole interaction. DB18C6 always shows high extraction selectivity for KClO4 over NaClO4, which is governed largely by the much greater K MLA value for K+ than for Na+. The K+ extraction-selectivity of DB18C6 over Na+ for perchlorate ions is comparable to that for picrate ions. By comparing this perchlorate system with the picrate one, the anion effects on the extraction-efficiency and -selectivity of DB18C6 for Na+ and K+ was discussed in terms of the fundamental equilibrium constants.